JPH05146192A - Driving circuit for dc brushless motor - Google Patents

Abstract

PURPOSE:To make it possible to drive a motor having high rotational speed with relatively low power consumption by driving the motor through a first driving circuit after stoppage thereof before reaching a predetermined rotational speed thereafter driving the motor through a second driving circuit. CONSTITUTION:An L signal is inputted from a rotational speed comparing means 2 to a FETQ7 after stoppage of a motor section 6 before reaching a predetermined rotational speed. Consequently, current flows through a driving coil L1 at the turn ON timing of transistors Q1, FETQ5. The current flows through a driving coil L2 and the FETQ5 into a FETQ8 where the magnitude of current is controlled. In other words, a first driving circuit 4 operates as a three-phase full-wave driving circuit. When the predetermined rotational speed is reached, an H signal is inputted to a FETQ7 and FETs Q4-Q6 are turned OFF. Consequently, current flows through a driving coil L1 at the turn ON timing of the transistor Q1. The current flows through the FETQ7 into a FETQ8 and a second driving circuit 5 operates as a three-phase half-wave driving circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is incorporated in, for example, a so-called notebook personal computer driven by a battery, which requires a particularly low power consumption, a low power supply voltage, a large driving torque and a high rotation speed. The present invention relates to a drive circuit of a DC brushless motor used for rotationally driving a disk of a small magnetic disk device of 5 inches or less.

[0002]

2. Description of the Related Art For example, a "sensorless brushless motor" filed by the same applicant (Japanese Patent Application No. Hei 1-13956).
No. 0) and "Driving method of brushless DC motor having no position detector" (Japanese Patent Application No. 2-146590) describes as follows.

First of all, a "sensorless brushless motor" is used to drive a motor by detecting a back electromotive force generated from a winding of the motor. A three-phase half-wave drive system in which electricity is applied in one direction from the end was used. On the other hand, the “driving method of a brushless DC motor having no position detector” uses a three-phase full-wave driving method in which each winding of three phases is energized from both directions.

By the way, the three-phase half-wave drive method has a simpler structure than the three-phase full-wave drive method, and thus the number of elements such as transistors is small, circuit loss can be reduced, and cost can be reduced. Since the back electromotive force is small, it has an advantage that it is easy to increase the maximum rotation speed.

On the other hand, the three-phase full-wave drive system has a larger starting torque and smaller torque ripple than the three-phase half-wave drive system.
It has the advantages of high efficiency and low power loss.

[0006]

As described above, both methods have advantages and disadvantages, and it cannot be generally said that either method is better. For example, the three-phase half-wave driving method has an advantage that the back electromotive force constant is small and the maximum rotation speed is large at a low voltage of 5 V or less, but has a disadvantage that the starting torque is small and the torque ripple is large. On the other hand, in the three-phase full-wave drive method, the starting torque and the counter electromotive force constant are large, and the torque ripple is small, but the maximum rotation speed is small, so a high speed rotation of about 3000 rpm is required at a low voltage of 3.5 V or less. It was difficult to use for. Therefore, a method of lowering the torque constant of the motor and increasing the input current can be considered.
The maximum electric power at the time of start-up becomes large, and in particular, in a hard disk drive device used for a so-called notebook personal computer or the like using a battery, there is a problem of insufficient battery capacity.

Therefore, an object of the present invention is to provide a drive circuit for a DC brushless motor which has the advantages of the three-phase half-wave drive system and the three-phase full-wave drive system.

[0008]

In order to solve the above-mentioned problems, according to the present invention, a switching element for selectively supplying a current is connected to a second terminal k which is the other end of each winding, and each winding is commonly used. A first drive circuit for supplying a current to both windings in both directions via the connected first terminal j and a switching element for selectively supplying a current to the second terminal k of each winding are connected to the second drive circuit. A second drive circuit that supplies a current in one direction between the terminal k and the first terminal j and a drive switching circuit that switches the drive circuit to either one of the first and second drive circuits are provided.

The drive switching circuit is configured to drive the first drive circuit from the time when the DC brushless motor is stopped to a predetermined rotation speed, and to drive the second drive circuit at a rotation speed exceeding the predetermined rotation speed. You can also do it.

[0010]

When the predetermined condition is satisfied, the drive switching circuit switches the driving of the motor to either the first or second driving circuit.

If the predetermined condition is a predetermined rotation speed,
The drive switching circuit switches the drive system of the motor so that the motor is driven by the first drive circuit from the time of stop to a predetermined rotation speed, and the motor is driven by the second drive circuit at the rotation speed exceeding the predetermined rotation speed.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram of an example of a drive circuit for a DC brushless motor according to the present invention, FIG. 2 is a block diagram of an example of the same rotation speed comparing means, and FIG. 3 is a circuit diagram of the first embodiment.
FIG. 4 is a circuit diagram of the second embodiment, FIG. 5 is a timing chart of the counter electromotive voltage waveform and a current flowing through the drive coil, FIG. 6 is a generated torque characteristic diagram, and FIG. 7 is the same power supply voltage vs. maximum rotation speed and FIG. 8 is a characteristic diagram of current consumption, and FIG. 8 is a characteristic diagram of the drive switching operation.

In FIG. 1, a drive circuit 1 for a DC brushless motor generates a rotation speed comparison means 2 for comparing the rotation speed of the motor with a preset rotation speed, and a drive switching signal based on the output signal of the comparison means 2. Drive switching circuit 3, a first drive circuit 4 and a second drive circuit 5, one of which operates according to the drive switching signal, and a motor section 6 to which a rotational force is given by the drive circuit 4 or 5. It

With this structure, the rotation speed comparison means 2 first compares the rotation speeds, and the drive switching circuit 3 operates either the first drive circuit 4 or the second drive circuit 5 according to the comparison result. Rotate 6.

The rotation speed comparison means 2 is generally composed of a microcomputer including an A / D converter and a timer, and an example thereof is shown in FIG. According to FIG.
Rotational speed comparison means 2 composed of a microcomputer or the like
Is, for example, a rotation speed detection unit 2a that detects a signal obtained by detecting a counter electromotive voltage generated during motor rotation from a coil of a motor (not shown), and counts signals such as pulses output from this detection unit 2a ( A counter 2b for counting), a timer 2c for stopping counting at a fixed time, and a comparator circuit 2e for comparing the count number of the counter 2b with the reference count number read from the reference value storage memory 2d. The output signal of the comparison circuit 2e is input to the drive switching circuit 3.

That is, the rotation speed of the motor section 6 is relatively compared by comparing the output of the counter 2b and the memory 2d. Therefore, the number of rotations required in advance, that is, 20 in this embodiment.
If a count number corresponding to 00 rpm is written in the memory 2d, a determination signal as to whether or not the rotation number exceeds 2000 rpm can be obtained as an output signal of the comparison circuit 2e.

FIG. 3 is a circuit diagram of a first embodiment of a drive circuit composed of the drive switching circuit 3 and the first and second drive circuits 4 and 5. Although a three-phase motor is used in this embodiment, the number of phases is not limited to three and any number of phases may be used as long as it is a DC brushless motor. In addition, parts similar to those of commonly used circuits are marked with symbols of parts, and description thereof is omitted.

The U-phase drive coil L1, the V-phase drive coil L2, and the W-phase drive coil L3 of the motor section 6 are selectively selected by PNP type transistors Q1, Q2, Q3 and FETs Q4, Q5, Q6 corresponding to switching elements. An electric current is supplied to rotate the motor unit 6. The drive switching circuit 3 is a switching circuit composed of the FET Q7, and the source side of the FET Q7 is connected to the drain side of the total current control FET Q8.

Next, the operation of this drive circuit will be described. First, the rotation speed of the motor unit 6 is 2000 rpm from the stop
Until the signal reaches Q.sub.2, the FET Q7 is supplied with an L (low) level signal from the rotation speed comparison means 2, and Q7 is off. Therefore, for example, at the timing when the transistor Q1 and the FET Q5 are turned on, the drive coil L
1, a current flows, and this current further flows into the FET Q8 via the coil L2 and the FET Q5. The magnitude of the current is controlled by this Q8. That is, this drive circuit operates as a three-phase full-wave drive circuit (hereinafter referred to as full-wave), and the first drive circuit 4 corresponds to this circuit.

On the other hand, the rotation speed of the motor unit 6 is 2000
When rpm is exceeded, an H (high) level signal is input to the FET Q7 from the rotational speed comparing means 2, and this Q7
Turns on. When Q7 is turned on, the FETs Q4 to Q6 are turned off by a drive coil control circuit (not shown). Therefore, for example, a current flows through the coil L1 at the timing when the transistor Q1 is turned on, and this current flows into the FET Q8 via the FET Q7. That is, this drive circuit is a three-phase half-wave drive circuit (hereinafter,
Half wave. ), And the second drive circuit 5 corresponds to this circuit.

FIG. 4 is a circuit diagram of the second embodiment of the drive circuit.
Transistors Q1 to Q3 and FETs Q4 to Q7 are used as switching elements as in the first embodiment, but analog switches S1 to S3 are provided on the input side of FETs Q4 to Q6 to control the currents flowing in the three phases in an analog manner. It is different from the first embodiment in that an analog switch S4 is also provided on the input side of the FET Q7.

FIG. 5 shows the control timings of the first and second drive circuits 4 and 5 shown in FIGS. 5B to 5G with respect to the counter electromotive voltage shown in FIG. .. (B) to (D) of the figure show the drive timing of the full wave (first drive circuit 4), and (E) to (G) of the figure show the drive timing of the half wave (second drive circuit 5). Here, the full-wave transistor and FE
The switching timing of TQ1 to Q6 is such that the counter electromotive voltage generated from the non-energized coil is detected by using the A / D converter incorporated in the microcomputer (not shown), so that two phases are energized and one phase is deenergized. The so-called 120-degree energization is used.

FIG. 6A shows a full-wave generated torque waveform, and FIG. 6B shows a half-wave generated torque waveform. From the circuit diagrams of FIGS. 3 and 4 and the timing chart of FIG. 5, if the resistance value for one phase is set to R and the loss of the circuit is ignored, in the full wave, the current is V / 2R because the two phases are energized. The waveform is a composite of two phases. Similarly, if the resistance value for one phase is set to R and the loss amount of the circuit is ignored, the current is V / R because current is applied to one phase in a half wave, and the current in one coil is doubled compared to the full wave. .. Therefore, the generated torque is not synthesized and the ripple of the waveform is increased as compared with the full wave, but the current is doubled, and the magnitude of the average torque is almost the same as the full wave. That is, the full wave requires only half the electric power to generate the same torque as the half wave.

FIG. 7 shows the relationship between the maximum number of revolutions ((A) in the figure) and the consumption current ((B) in the figure) with respect to the power supply voltages of the three-phase full wave and the three-phase half wave. As an example, this shows a drive circuit of a spindle motor that rotationally drives two disks of a 2.5-inch small hard disk drive (HDD), and the maximum current at startup is approximately 600 in the case of full wave.
It is approximately 1.2 A in the case of mA and half wave.

As described above, the torque at start-up is almost the same for the full wave and the half wave, but the maximum rotation speed with respect to the power supply voltage is larger in the half wave than in the full wave as shown in FIG. Is about 1.5 times in the large area. Moreover, the same figure (B)
It can be seen that the current at that time is significantly larger in the half-wave than in the full-wave. The maximum rotation speed of the half wave is higher,
This is because the voltage applied to the coil to obtain the maximum rotation speed is the power supply voltage minus the counter electromotive voltage generated in the coil, and the half wave has a smaller counter electromotive voltage.

FIG. 8 is a characteristic diagram showing the operation when switching between full-wave and half-wave driving, and this switching operation is performed when the power supply voltage is less than 3.5V. That is, generally, an HDD operating at 3 to 5V includes a microcomputer (not shown) having a reference voltage generation circuit and an A / D converter built therein, and the power supply voltage is A / D converted with respect to the reference voltage. A full-wave or half-wave drive circuit is selected to measure and set the rotation speed of the spindle motor to the rated rotation speed of 3200 rpm. By the way, as can be seen from FIG. 7A, the power supply voltage is approximately 3.5V.
Since a rotation speed of 3200 rpm can be obtained even with a full wave in the above case, in this case, only the full wave drive circuit is used from startup to rated rotation, and the drive according to the present invention is applied when the power supply voltage is less than 3.5V. I used a circuit.

According to FIG. 8, the rotational speed is about 20 from the start.
2000r by operating the full-wave drive circuit up to 00rpm
When it exceeds pm, it can be seen that the circuit is switched to the half-wave drive circuit and operated to obtain the rated rotation speed of 3200 rpm.

As described above, the present invention is characterized in that the drive circuit of the DC brushless motor is configured so as to use the advantages of the three-phase full-wave drive circuit and the three-phase half-wave drive circuit in combination. That is, since the three-phase full-wave driving circuit has a large starting torque and a small torque ripple, the maximum current is small at the time of starting by using this full-wave driving circuit from the time of starting to a predetermined rotation speed, for example, up to about 2000 rpm. Therefore, the maximum power consumption can be reduced. On the other hand, 3
The half-wave drive circuit has a small back electromotive force constant and a large maximum rotation speed. Therefore, after the rotation speed exceeds 2000 rpm, the half-wave drive circuit rotates relatively stably at a high rotation speed even when the power supply voltage is about 3V. Can be driven.
Although the switching element is composed of the PNP type transistor, it may be composed of the NPN type transistor, or may be composed of another amplification element such as FET.

Further, only one FET is added to the conventional drive circuit as a drive switching element, and drive control is performed by almost software, and since many parts can be commonly used, additional software is added. The increase in memory for the wear is also small. Therefore, the present invention can be applied to a small motor, and the cost can be reduced.

[0030]

Since the drive circuit of the motor is configured to select and use two drive circuits, it is possible to combine portions having good characteristics of each drive circuit. Therefore, it becomes possible to obtain a motor having a large number of rotations with relatively low power consumption and by adding a relatively simple circuit, which is suitable for downsizing of the motor and at the same time cost can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an example of a drive circuit of a DC brushless motor according to the present invention.

FIG. 2 is a configuration diagram of an example of the rotation speed comparison unit.

FIG. 3 is a circuit diagram of the first embodiment.

FIG. 4 is a circuit diagram of the second embodiment.

FIG. 5 is a timing chart of the counter electromotive voltage waveform and a current passed through a drive coil.

FIG. 6 is a generated torque characteristic diagram of the same.

FIG. 7 is a characteristic diagram of the same power supply voltage vs. maximum rotation speed and consumed current.

FIG. 8 is a drive switching operation characteristic diagram of the same.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Drive circuit of DC brushless motor, 2 ... Rotation speed comparison means, 3 ... Drive switching circuit, 4 ... First drive circuit, 5 ... Second
Drive circuit, 6 ... Motor part, j ... 1st terminal, k ... 2nd terminal, L1-L3 ... U-phase-W-phase drive coil, Q1-Q3 ...
PNP type transistor, Q4 to Q8 ... FET, S1 to S
4 ... Analog switch.

Claims (2)

[Claims] 1. A drive coil comprising a plurality of windings and having a first terminal j, one end of which is commonly connected, and a magnetic field generated by supplying a current to the drive coil In a drive circuit of a DC brushless motor that generates a rotational force by interaction with a magnetic field generated from a magnetized drive magnet, a switching element that selectively supplies a current to a second terminal k that is the other end of each winding is provided. First connected to supply current in both directions to the two windings through the first terminal j
A driving circuit and a second driving circuit for connecting a switching element for selectively supplying a current to the second terminal k of each winding and supplying a current in one direction between the second terminal k and the first terminal j; And a drive switching circuit for switching the driving circuit to one of the first and second driving circuits.
C brushless motor drive circuit. 2. The drive switching circuit is configured to drive the first drive circuit from the time when the DC brushless motor is stopped to a predetermined rotation speed, and to drive the second drive circuit at a rotation speed exceeding the predetermined rotation speed. The drive circuit for the DC brushless motor according to claim 1, wherein